Recently, various techniques for flattening a vehicle fuel tank have been developed to meet the needs for a roomier passenger compartment. A flattened fuel tank has a larger dead space in an upper portion thereof which may cause a problem of a reduction in a substantial filling amount of the fuel tank. To solve such a problem, a technique for reducing the dead space through the flattening of a fuel shutoff valve structure has been proposed (see, for example, Japanese Unexamined Patent Application Publication No. 2006-183596).
However, if the technique disclosed in Japanese Unexamined Patent Application Publication No. 2006-183596 is applied to further flatten the fuel tank, a fuel shutoff valve may become submerged in fuel in the fuel tank when the vehicle is inclined, causing a fuel outflow to a canister.